The Novikov Self Consistency Principle
by JustDawdling
Summary: A little-known fact: when Harry was killed by Voldemort in the Forbidden Forest, he was forcibly thrown back to the year 1977 to ensure that he was sent to King's Cross the second time around. Possible AU, but should be technically canon-compatible.


**A/N: This story will update very slowly. I was tired of writing my other one and this makes me want to write on it more.**

Chapter 1

**A Stitch In Time Saves Nine**

The Novikov Self-Consistency Principle—proposed by its namesake, Russian physicist Igor Novikov—claims that time paradoxes are impossible, as any event that would result in a paradox has a zero probability of occurring.

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No matter how thoroughly any witch or wizard tries to prepare themselves for being struck with the Killing Curse, it is impossible to truly be ready when the green light strikes them down. When Harry James Potter, age 17, was impacted by the Killing Curse cast by Tom Marvolo Riddle, age 71, on 2 May 1998, his resignation to inevitability was inadequate in this respect. The feeling of being lifted high off the ground even as his body fell down onto it was too surreal to properly describe.

He was, after all, dead. Or so he thought.

The piece of soul lodged in his martyr complex filled (and by all definitions of self-preservation "insane") head would not protect him from most forms of death. Decapitation, poisoning, heart attack, stroke, hell, a bullet in the brain would easily take care of meddling hero wizard Harry Potter. Even spells that inflict bodily harm like the Bone-Breaker Curse and the Blasting Curse could, if strong enough, kill him. But because the Avada Kedavra is a purely magical cause of death, with no physical effects other than the whole being dead issue, the Horcrux was incidentally able to absorb death. If only Voldemort had pointed his wand at Harry's head and cast the Reductor Curse until it turned into an amorphous pile of brain and scattered skull shard goop…

But whatever, that's pretty anticlimactic.

So Harry gets nailed by the sickly glowing greenish light, right?

Right.

Most people know the general outline of the story that follows. Harry wakes up, kills the bad guy, everyone ends up happy, big hurrahs all around. What most people _don't_ know is that it's what happened the second time around, not the first.

The first time, there was no Elysian King's Cross station in the sky.

The first time, there was no meeting with a schizophrenic representative of Harry's mind taking the appearance of his Headmaster.

The first time, there was no resurrection, no return, no triumph.

The first time, there was only darkness for the longest time. Then came a shiver, a shudder, and the dawn of a new day. It was exactly twenty-one years prior, 2 May 1977. Why twenty years and another on top of it? Perhaps it's because seven and three are both magical numbers and when you multiply them… or maybe magic is as arbitrarily coincidental as possible. That seems more likely given his history.

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Actually, the dawn was of the day 3 May 1977, as Harry laid unconscious the entire night since his encounter with the Killing Curse. He was motionless, prone in the exact same spot where he had been killed twenty-one years later. How did he manage to sleep in the Forbidden Forest without being eaten? Hell, how did he even get here?

Arbitrarily coincidental as possible.

Of course, explained in as much detail as possible while still being brief, it was the confluence of powerful magics—the Horcrux, the Deathly Hallows, the Killing Curse—all coming together and creating a magical coexistence paradox. Unlike time paradoxes (which, as we know thanks to Novikov, are merely the product of fiction writers' imaginations), magical coexistence paradoxes are very real. Harry was, in the eyes of magic, simultaneously alive and dead. To resolve this paradox, he was thrown backwards in time to create the conditions necessary for the events of 2 May 1998 the Second to occur. Thanks Dr. Novikov!

In any event, Harry woke up. He stretched, his stiff joints aching from lying in the same casket-dead, rigor mortisish position for several hours. A light groan escaped his throat as several bones popped as he flexed his shoulders, elbows, and then knees. He brushed the back of his head, shaking the leaves out of his mussed hair. He rubbed his eyes and tweaked his glasses slightly, setting them in their familiar position upon his nose. Lightly massaging his sore neck, he stood and surveyed his surroundings.

"Where am I?"

Turning in a full circle, he caught sight of the trees, most of them hundreds of years old. A charm of finches flew overhead as he squinted in the early morning sunlight. "Looks like the Forbidden Forest, but… different."

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Arbitrarily coincidental as possible. This was the first time Harry would, if he could, thank the magical world for being in such stagnation. The Forbidden Forest was essentially the same, Hogwarts hadn't changed a tick since who-knows-when, Diagon Alley was filled with the same stores, and virtually no spells of any significance were invented in the twenty years and three hundred and sixty-four days between now and Harry's death. Fortunate, as Harry could remember absolutely nothing that had changed in any significance since his birth.

This was much simpler to understand. After all, none of those things existed in 2 May 1977 (or 3 May 1977 for that matter), so his mind was incapable of recalling them. People in particular were a problem, as no people existed as Harry had seen them except for one. The only person Harry remembered was Harry—and only Harry. No James, no Potter, just Harry. After all, Harry James Potter hadn't been born yet. He was just a guy named Harry. Oh, his personality was intact—hero complex (the infamous "saving people thing"), love of broom-riding, attraction to redheads, dislike of cupboards—but it was on a whole new Quidditch pitch this time: 1977.

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So, this guy named Harry stumbled out of the Forbidden Forest, his holly wand at the ready. He again sensed an odd familiarity with his surroundings.

"This is… near Hogwarts."

_Hogwarts. _"Heh."_ That's a funny name for a magic school. Magic school? Oh, right. You're not just holding a plain stick like a weapon, idiot. It's a wand._

As Harry walked slowly towards the castle, he spotted a small building. _That's a hut. Somebody lives there, but I can't for the life of me remember who._

The person he didn't know walked out of the hut, wielding a devastating-looking crossbow and had a suspicious look on his face. It would intimidate most people coming from a man of his stature, but Harry wasn't most people. The two closed to within earshot.

"Stop righ' there! Who're ya?"

Harry shrugged. "I'm Harry. Who're you? And can you please put that thing down?"

Hagrid hesitated, but his trusting side got the better of him and he slowly lowered the weapon, though not taking his eyes off Harry. "Name's Rubeus Hagrid, gamekeeper here at Hogwarts. Thought ye were a student here fer a moment, but up close... nah, ye don't look so much alike up close. Yer face is rounder, ain't as strong-jawed, longer hair too—and o' course the glasses."

Harry shrugged. "Sorry Mister Gamekeeper, but I'm afraid I don't know who you're talking about. You went and rambled a bit there."

At least he had the decency to look sheepish about it. "Sorry 'bout that. Call me Hagrid! Ye said yer name's Harry?" Harry nodded. "Ye got any other names?"

Hagrid smiled cheekily at his own lame attempt at humor. It was meant to be rhetorical. "No."

"I—whaddya mean ye don't have any other name? What's yer dad's last name?"

"I… I don't know. I sorta just woke up here a half hour ago and I can't remember much."

Hagrid's eyes bulged with surprise, like there were little eye pixies pushing on them from behind in an effort to escape. They didn't get out this time. Maybe next time. "Ye don't remember yer own name? Oh, that's no good, not right now. Times're bad, real bad, wizards with no heritage are bein' hurt 'n killed. Ye sure ye don't know yer name? Maybe yer a pureblood?"

Harry shrugged. The term pureblood was familiar. "Yeah. I think so, at least. Can't remember who they are, but I know Mum was a wizard and Dad was a wizard."

"Ye don't remember yer own parents? Merlin's beard. If ye got a vault at Gringotts ye can get the goblins to give ye a blood test, see if ye own any vaults, figure out who ye are. Say, I bet the Headmaster could help! Albus Dumbledore is a great wizard, he'll surely help. I'll bring ye up to him Harry, c'mon with me," Hagrid said, beckoning Harry to follow him to the castle. Harry shrugged and shuffled along behind Hagrid. He didn't implicitly trust the towering man before him, but it was the closest thing he had to a ticket inside the castle.

Harry found something comforting about Hogwarts, like it was the only place he had ever called home. 4 Privet Drive hadn't been built yet, as it were. It was still under construction, to be purchased by Vernon and Petunia Dursley later in the year.

Hagrid led him to the statue of the gargoyle and declared the password quite loudly ("Meticulously-Made Malted Milk Balls"), coercing the gargoyle to allow them passage. He rapped loudly on the door and a voice could be heard from inside, "Come in, Hagrid!"

He opened the door hesitantly (well, as hesitantly as a lumbering half-giant can) and poked his head inside. "Headmaster? Can I talk to yeh for a minute?"

"Certainly, dear friend. And you've brought a guest, I see! Who might you be, young man?"

The unlikely pair stepped inside. "I was hopin' ye could help us figure tha' out. 'e said he woke up in the Forest this morning and doesn't remember who 'e is. 'is name is Harry and he's a wizard, pureblood at that."

Dumbledore examined Harry carefully. "Is that so? Do you remember your parents' names?"

"No, Mister Dumbledore—"

"Please, Harry, Professor will do fine."

"A-all right, Professor. I've been piecing a few things together. When I woke up, I knew I was in the Forbidden Forest and I know this is Hogwarts. I know I'm a wizard, but I don't know how I got here or where I'm from. All I know is that Hogwarts feels like… home," Harry said, suddenly looking a bit nervous. "Can you understand that?"

Dumbledore smiled, eyes dancing with delight. "Indeed I can, Harry," he said, looking Harry in the eye. A flash of confusion passed his face as Harry felt a light brushing sensation at the base of his skull, but both disappeared before Harry could figure out whether he had just imagined it.

The Headmaster took a half hour to ask a few probing questions, but Harry had no useful information. Time after time, Harry shrugged and replied with an "I don't know" or an "I _still_ don't know" if he felt like the Headmaster was being repetitive. After a while, he finally got to something fresh. "I have an idea. Could you perhaps demonstrate your knowledge of spells for me?"

Harry grinned. Answering questions he had no way of knowing wasn't something he could do. This was something he could do. He showed off some of the spells he remembered, but had the presence of mind to keep some of his knowledge discretely close to his chest. He had a bad feeling in the pit of his stomach when he thought about casting spells like Fiendfyre or the Bone-Breaker Curse, but had no such restraints about finishing with,

"_Expecto Patronum!_"

Dumbledore and Harry both looked shocked at what they saw. Dumbledore was surprised that such a young man could conjure a corporeal Patronus. Harry was shocked at his Patronus itself. He realized he didn't have any properly strong memories to call on and he could feel how weak it was. It could only fend off a single Dementor at best. And the shape was all wrong. He didn't know why, but he could _feel_ it, deep in his bones. It took him a moment to realize that his Patronus was the first animal he'd seen after coming to in the Forest.

"A finch? That's... stupid," Harry said, not realizing until it left his mouth how silly he sounded.

Dumbledore looked at Harry curiously. "Is that not what you expected?"

Harry shrugged. "I'm not sure what I expected, but it wasn't that. A finch was the first thing I saw when I woke up this morning, that's all." He paused. "My Patronus is usually much stronger. I… I'm not sure how I know that."

Dumbledore hummed lightly to himself. "Most curious. I would postulate that since it is the only animal you remember with any significance, your magic filled the finch in as your Patronus. I am quite sure your Patronus will change over time, whether your old memory returns or you simply fill it in with new ones."

Dumbledore paused and popped a lemon drop in his mouth. Harry politely declined when he gestured toward the bowl. "Harry, your skills are quite impressive, though admittedly lacking in a few areas. You have quite obviously been taught a good foundation as a wizard, regardless of where you learned it. It is too late for this term, but if you wish you may attend Hogwarts in the fall as a seventh year student and take your NEWTs with the rest of the students. Would that be an acceptable arrangement?"

Harry's face lit up. "That'd be brilliant, sir. I'd like that very much."

"Then it is settled," Dumbledore said with a twitch of a smile on his face. "You will attend Hogwarts next term after taking your OWLs next month. Do you have any plans until then, Harry?"

"Well," Harry said, then paused. He hadn't thought of that. "I suppose I'd like to get a job in Diagon Alley, something to do, you know?"

Dumbledore nodded, then smiled with a twinkle in his eye. "Yes, the eagerness of youth to go out into the world and do whatever they can, no matter how great or how insignificant," he said, tapping a lemon drop with his wand and handing it to Harry. "Here, Harry."

"Oh, no sir, I don't—"

"Ah, I am afraid I wasn't clear. This is a portkey that will become active in a month from now and will transport you to the outskirts of Hogwarts. On the day of your OWL, simply hold the lemon drop and speak the trigger phrase. It is the same one that Hagrid had to give it to the gargoyle to enter, do you remember it?"

Harry nodded and rolled his eyes. "It'd be hard to forget such a grandiose password even if my head were full of memories, sir."

"Very good! You may use my fireplace to get to Diagon Alley if you like, Mister Potter. Do you remember how to use the Floo?"

Harry was unreasonably irritated by the question. "Of course, sir. I've got amnesia, but I'm not stupid all of a sudden," he said. A beat skipped. "Was that inappropriate?"

Dumbledore chuckled aloud. "Ah, not at all, Harry. I should have known better. As much as I would like to speak with you in greater detail, I must confess that I do have a school to run, though it does seem to run itself at times. If that will be all?"

"Yes, sir. I'll be going now. School can't run without you, I'm sure… unless it runs itself," he quipped, stepping over to the fireplace and taking a bit of Floo powder.

"Oh, and Harry?"

Harry turned, powder still pinched between his fingers. "Sir?"

The Headmaster had a mischievous look about him that was not being suppressed nearly well enough. "If you need a pureblood surname to use while you work out your true identity, try Peverell."

Harry saw the gleam in the Headmaster's eye and suddenly felt nervous. "Peverell, sir?"

"The Peverell line has been extinct for some time," the Headmaster elaborated. "The few who have heard of the name will likely be too excited to discover a living Peverell to question whether you actually are a Peverell or not."

"If you say so, sir," Harry said. With that, he threw the Floo powder into the fire. "Diagon Alley!"

As Harry disappeared into the flames, Dumbledore turned to Hagrid, who had patiently watched the hour long session in a startling degree of silence. "Hagrid, my friend. What do you think of the boy?"

Hagrid smiled. "Once he got over not knowing who he was, he turned into an awful cheeky bugger didn't he?"

"Indeed he did," Dumbledore affirmed, smiling wanly at the boy's attitude. "However…"

Hagrid noticed how the aged wizard trailed off. "Professor?"

"It was strange, Hagrid. I swept him with a light Legilimency probe, nothing invasive of course," he assured the half-giant. "I daresay it was unlike anything I've ever seen. I did not feel anything."

"Like…" Hagrid said, a hint of fear creeping into his voice, "like he were a ghost?"

"Oh no," Dumbledore replied quickly, with a soothing tone, "nothing like that. I have encountered ghosts, poltergeists, and Occlumencers over the years, but this was nothing like that. He wasn't resisting at all. It was as if he simply were not there, as if he didn't exist."

"Er," Hagrid said eloquently, "so what's that mean, Headmaster. Is he… on our side?"

"Oh yes," said Dumbledore. "He is not one of their type. I must admit I do pride myself on being an excellent judge of character, magical or not. No, all this is just curious. Most curious indeed."

But, try as he might, the wizened Headmaster couldn't even piece together a clue as to why, whenever he reached out with his magic, the young man he met existed—or didn't exist—as a void in the world.


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